Instrument for a centrifugal separator for detecting the presence of a body and rolling mill provided with such an instrument

ABSTRACT

An instrument for detecting the presence of a body, comprising a detector (2) and a housing (1) in which the detector (2) is accommodated. The housing (1) is provided with at least one guide passage (6) for transmission to the detector (2) of one or more signals originating from the body. The housing (1 ) is also provided with means for supplying a gas flow (8), for example, compressed air, and a means for discharging at least a part of said flow through the guide passage (6) in such a way that, during operation at least a part of the cleaning gas leaves the housing (1) via the transmission passage (6). At the same time the invention relates to a rolling mill provided with means for determining velocities of the products to be rolled. The means for determining recording velocity comprises at least two of the instruments above and a processing unit which is linked to receive the signals from those instruments for ascertaining the velocity of a product detected by the instruments.

The invention relates to an instrument for detecting the presence of abody, comprising a detector and a housing in which the detector isaccommodated.

One known type of instrument is based on the principle of thermalradiation detection from a body. However, detection methods using otherwave ranges are also known. Such a device comprises a housing providedwith a least a transmission passage aimed in the direction of the bodyto be detected suitable for guiding to the detector one or more signalsoriginating from the body. An instrument of this type is used in thepractice of continuous casting. Applications in rolling millinstallations are also known. Also applications in the field ofmeasuring temperatures in hostile environments are known. Reference ismade to U.S. Pat. No.5,000,580 and DE-C-895,161. U.S. Pat. No. 5,000,580discloses a radiation pyrometer suitable for detecting the presence of abody, which basically comprises a detector (1) in a housing having aguide passage for transmission of radiation from the body to bedetected, and is equiped with a gas purge system for directing cleansinggas (air) onto a lens and down the guide. At the distal end of the guidean additonal gas injection system is arranged of which one part definesa conduit about the end of said guide, and another part defines a slotfrom which gas (air) is discharged into the conduit away from thehousing and about the guide passage.

A similar configuration is disclosed in DE-C-895,161. Whereas in U.S.Pat. No. 5,000,580 both puree and injection system are provided withpressurized gas, in DE-C-895,161 injection of gas takes place only via aseparate inlet of the additonal injection system resulting in suction ofgas through the purge system.

Further prior art (U.S. Pat. No. 4,738,528) shows a method of cleaning apyrometer lens by directing purge aire spirally inward over the lenssurface such that a vortex is formed by the spiral air flow to increaseeffectivity of the cleaning action.

U.S. Pat. No. 4,784,491 teaches the application of pitched grooves orscrew threads in the walls of a gas channel to induce a swirling flow toprotect optics against debris and moving particles in the air.

GB-A-1,114,682 proposes the application of a head for a detectioninstrument, including tangential gas inlet for supply of cleaning gasalong the sight-way of the instrument.

In this application the instrument serves to detect the presence of aslab to be rolled out for purposes such as bringing the mill stands ofthe rolling mill up to the desired angular velocity on time and formaking other setting adjustments. Instruments of the kind referred to inthe preamble are also used in rolling mills provided with a reversingrolling unit. In a reversing rolling unit a slab is rolled out in anumber of backward and forward motions into an intermediate productwhich is suitable for being rolled out to a desired finished rollingthickness in a finishing train. It is important in the use of such areversing rolling unit to detect not only when the slab to be rolled isapproaching the roller but also when it is leaving the roller. Valuableproduction time may be saved with this information, given that, forexample, detecting the slab leaving the mill stand offers theopportunity of reversing the drive direction of that mill stand as earlyas possible.

There is a problem in the applications mentioned above in that theinstrument has to work in highly contaminated surroundings whichadversely affect the operation of the instrument especially in respectof the temperature conditions. Consequently, the known instrumentrequires a great deal of maintenance. These aggravating conditionsinclude the continual presence of surrounding air saturated withmoisture as a result of the cooling water sprayed onto the rollers andthe high pressure descaling water for removing the scale from the slabto be rolled. In addition much dirt is present in the surrounding air inthe form of iron oxide or oil. Also associated with this is the problemthat, in terms of measuring (recording) roller technology, the knowninstrument for detecting the presence of a body is, in itself, difficultto use in this application, given that the air is saturated withmoisture in the form of steam.

The invention is intended to offer a solution to the above-mentionedproblems and to achieve further advantages which shall be illustrated inthe following.

The invention provides an instrument for detecting the presence of abody, comprising a detector and a housing, in which the detector isaccommodated, said housing being provided with at least one guidepassage for transmission to the detector of signals originating from thebody comprising means for supplying a gas flow and means for directingat least part thereof through said guide passage, and further comprisinga device with an inner and an outer element, the inner element providinga central throughflow conduit surrounding said guide passage, and saidouter element at least partially arranged about the inner element andcooperating therewith to form a slot for discharge of gas into saidconduit away from The housing and around said passage, and ischaracterised in that the instrument is further provided with acentrifugal separator for separating the cleaning gas into clean andpolluted fractions,whereby the means of supplying the cleaning gas areconnected close to the outer periphery of the centrifugal separator andat least a part of the means for discharging the said cleaning gas isconnected adjacent to the centre of the separator, whereby means for thedischarge of the polluted fraction are connected to the said device fordischarge of the said polluted fraction through said slot. According tothe invention the desired cleaning may be realised using cleaning gaswhich itself is contaminated. Such gas is present, for example, in thelocal compressed air supply network of a hot-rolling mill. This supplynetwork makes use of surrounding air present in the rolling mill andconsequently it is contaminated, among other things, by oil particlessuspended in the air.

With the centrifugal separator proposed the cleaning gas coming fromthat supply network is split into a pollutant rich fraction and afraction with a low pollutant level. The lower pollutant fractionobtained with the separator may be used for discharging via thetransmission passage.

Preferably, at the beginning of the transmission passage the centrifugalseparator should be provided, adjacent its centre, with deflector meanspositioned transverse To the direction of the movement of the cleaninggas for reducing the rotational flow energy in the cleaning gas. Thiscounteracts the strongly circular motion of the cleaning gas as itleaves The centrifugal separatorvia the transmission passage so that thecleaning gas is conveyed in an essentially straight path along theTransmission passage.

In a preferred embodiment of the instrument in accordance with theinvention the transmission passage is provided with a constrictionpreferably close to its end remote from the detector. Thus the cleaninggas attains its highest exit rate at the outer end of the transmissionpassage and consequently the entry of dirt into the housing is furtherimpeded.

It has been found that the line of sight for the outflow of the cleaninggas from the transmission passage is capable of having a sighting rangeof approximately three meters away from the housing. It is believed chatthis is brought about because the gas flow which is generated by meansof the device and which surrounds the gas flow out of the transmissionpassage, protects the latter against turbulence (reversal) caused bydirt and steam in the surroundings. It is preferable for the dischargeslot to be provided on the end of the device nearer to the housing andto be directed away from the housing cowards the central conduit of thedevice. Thus the gas leaving the discharge slot via the central conduitof the device creates a local pressurised region of the side of thedevice closest to the housing. As a result; of this the surrounding airfrom that side is forced along through the central conduit of the deviceso that a large air movement occurs which surrounds the centrallysituated gas flow from the transmission passage and protects it againstturbulence.

In a preferred embodiment the transmission passage extends through thecentral conduit of the device and terminates in the region of an end ofthe central conduit further from the housing. This embodiment is foundto give especially good result in terms of the distance from which theinstrument may still be used to detect a body. The reason for this isthat in this embodiment the central line of sight, resulting from thegas outflow from the transmission passage, remains unchanged for aparticularly long time by any turbulence of that flow.

An alternative embodiment is characterised in that the device ispositioned beyond and adjacent to the outlet mouth of the transmissionpassage. This embodiment is preferable for use in very contaminatedsurroundings.

The invention described in the foregoing is as yet described only interms of application with an instrument which comprises only onedetector, though it is not limited to that. The invention is alsoembodied in an instrument in which the housing is also provided with asignal transmitter and a further transmission passage for directing asignal from the transmitter to the body to excite the signal to bereceived by the detector. The transmission passage forms at least a partof the discharge means for the cleaning gas flow.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings.

FIG. 1 shows the instrument in accordance with the invention in a firstembodiment.

FIG. 2 shows the instrument in accordance with the invention in a secondembodiment.

FIG. 3 shows a cross-section through the centrifugal separator of theinstrument in accordance with the invention.

Corresponding reference numerals in the figures indicate correspondingparts of the instrument.

In FIG. 1 and 2 an instrument is shown comprising a housing (1), adetector (2) in the housing (1), which detector (2) is mounted behind alens (3). Detector (2) is for example an infrared sensitive elementwhich emits an electrical signal if it is activated by infraredradiation, The said electrical signal is led via a cable (4) to furtherprocessing equipment.

On the side of the lens (3) the housing (1) is provided with acentrifugal separator (5) in which cleaning gas is processed in orderfirstly for it to help keep clean the surface of the lens (3) andfurther to help keep clean a transmission guide passage (6) that extendsfrom the lens surface (3) to an end or mouth (7) close to an outerboundary of the housing (1).

Cleaning gas is supplied into the centrifugal separator (5) via a feederpoint (8). To this feeder point (8) may be connected, for example,compressed air that may be contaminated. In the centrifugal separatorthe compressed air supplied via feeder point (8) is brought int acircular motion so that any dirt particles present in the compressed airconcentrate on the outer circumference of the centrifugal separator (5)and as a result of this the compressed air moving close to the lenssurface (3) is comparatively clean and can clean the lens surface (3)effectively because of the rapid circular motion.

Near the transmission passage (6) the centrifugal separator (5) isprovided at its centre with plates (9) (see also FIG. 3) which slow downthe circular motion of the cleaning gas supplied via feeder point (8)and cause an essentially straight motion of the cleaning gas into thetransmission passage (6). The cleaning gas leaves the housing (1) viatransmission passage (6) and its mouth (7). Preferably the mouth (7) ofthe transmission passage is also provided with a constriction in orderto effect a higher outflow rate near to this outer boundary of theinstrument.

At the same time the instrument is provided with an device (19)comprising a first element (11) and a second element (12) which, actingjointly, define a discharge slot (13). The device (19) is provided witha feeder point (14) for a gas which can leave the device (10) in adirection away from the housing (1) through the discharge slot (13) andvia a central conduit (15) of the device (10). The gas that leaves thetransmission passage (6) is then surrounded by the gas that leaves thedevice discharge slot (13) through the central conduit (15) of thedevice (10). This creates a laminar flow whereby an extended line ofsight is formed from the end of transmission passage (6). The line ofsight corresponds with the gas outflow from transmission passage (6) andis maintained by the gas flow which surrounds the gas outflow fromtransmission passage (6), and which is induced by the gas escaping outof discharge slot (13). The belief is that this is particularlyencouraged because the gas that leaves the discharge slot (13) via thecentral conduit (15) of the device (10) creates a local pressurisedregion on the side of the device (10) near the housing (1). As a resultthe surrounding air from that side is forced along through the centralconduit (15) of the device (10), so that a large air movement occurs.This surrounds the centrally situated gas flow out of the transmissionpassage (6) and protects it against turbulence (reversal).

FIG. 1 shows chat the mouth (7) of the transmission guide passage (6)opens out adjacent to the side of the central conduit (15) of the device(10) facing away from the housing (10). This embodiment is found to beparticularly effective for .extending the sight passage over a longdistance from the end of transmission passage (6).

An alternative embodiment is shown in FIG. 2 whereby the mouth (7) ofthe transmission passage (6) is positioned just in front of the centralconduit (15) of the device (10). This embodiment is found to be veryeffective in highly contaminated surroundings.

The feeder point (14) of the device (10) is connected, by means of arigid connection pipe (16) to the discharge point (17) for therelatively polluted fraction of the cleaning gas originating from thecentrifugal separator (5). This makes it possible to ensure fixedpositioning of the device (10) relative to the housing (1).

The invention is not limited to the example embodiments described in theforegoing but may be applied with equal success with instruments, which,instead of a single detector (2), are provided at the same time with asignal transmitter and another transmission passage suitable for guidinga signal originating from the transmitter in the direction of the bodyto be detected. The transmission passage in doing so forms at least apart of the means of discharge of the cleaning gas. The signal issuitable for causing another signal to be generated from the body, thissignal being suitable for being detected by the detector.

We claim:
 1. An instrument for detecting the presence of a body,comprising a detector (2) and a housing (1), in which the detector (2)is accommodated, said housing (1) being provided with at least one guidepassage (6) for transmission to the detector (2) of signals from thebody, and with means for supplying a gas flow (8), and means fordirecting at least a part of said flow through the guide passage (6)such that, during operation, at least a part of the gas flow leaves thehousing (1) via the guide passage (6), and further comprising a device(10) entailing an inner element (11) providing a central throughflowconduit (15) surrounding the guide passage (6) or an extension of thedischarge flow path therefrom, and an outer element (12) at leastpartially arranged about the inner element (11), said elementscooperating in defining a slot (13) for discharge of gas into saidconduit in a direction away from the housing (1) and around said passage(6) or said extension, characterised in that it is provided with acentrifugal separator (5) for separating the gas into a clean and apolluted fraction, and wherein gas supplying means (8) are connectedclose to the outer periphery of the centrifugal separator (5), and thegas directing means comprises a connection adjacent the centre of saidseparator (5), whereby means for the discharge of the polluted fractionare connected to said device (10) for said discharge of said pollutedfraction through said slot (13).
 2. The instrument according to claim 1,wherein the centrifugal separator (5) is provided adjacent its centrewith deflector means (9) positioned transverse to the direction of flowof the gas for reducing the rotational flow energy of the gas.
 3. Theinstrument according to claim 1, wherein the guide passage (6) extendsthrough the central conduit (15) of the device and terminates in theregion of an end of the central conduit further from the housing.
 4. Theinstrument according to claim 1, wherein the device (10) is positionedbeyond and adjacent to an outlet mouth (7) of the guide passage (6). 5.The instrument according to claim 1 wherein the gas flow directing meansare provided for directing a further part of said housing gas flow forsaid discharge through said slot (13).
 6. The instrument according toclaim 1 provided with a centrifugal separator (5) for separating the gasinto a clean and a polluted fraction, and wherein the gas supplyingmeans (8) is connected close to the outer periphery of the centrifugalseparator (5), and the gas directing means comprises a connectionadjacent the centre of said separator (5), wherein means for thedischarge of the polluted fraction is connected to said device (10) forsaid discharge of said fraction through said slot (13).
 7. Theinstrument according to claim 6, wherein the centrifugal separator (5)is provided adjacent its centre with deflector means (9) positionedtransverse to the direction of flow of the gas for reducing therotational flow energy of the gas.
 8. The instrument according to claim1 wherein the housing (1) is provided with a signal transmitter and afurther guide passage for directing a signal from the transmittertowards the body to excite said signal to be received by the detector,said further passage forming at least a part of the directing means forthe gas flow.
 9. The instrument according to claim 4, provided with acentrifugal separator (5) for separating the gas into a clean and apolluted fraction, and wherein the gas supplying means (8) is connectedclose to the outer periphery of the centrifugal separator (5), and thegas directing means comprises a connection adjacent the center of saidseparator (5), wherein means for the discharge of the polluted fractionis connected to said device (10) for said discharge of said fractionthrough said slot (13).
 10. The instrument according to claim 2, whereinthe guide passage (6) extends through the central conduit (15) of thedevice and terminates in the region of an end of the central conduitfurther from the housing.
 11. The instrument according to claim 2,wherein the device (10) is positioned beyond and adjacent to an outletmouth (7) of the guide passage (6).
 12. The instrument according toclaim 2, wherein the gas flow directing means are provided for directinga further part of said housing gas flow for said discharge through saidslot (13).
 13. The instrument according to claim 3, wherein the gas flowdirecting means are provided for directing a further part of saidhousing gas flow for said discharge through said slot (13).
 14. Theinstrument according to claim 10, wherein the gas flow directing meansare provided for directing a further part of said housing gas flow forsaid discharge through said slot (13).
 15. The instrument according toclaim 4, wherein the gas flow directing means are provided for directinga further part of said housing gas flow for said discharge through saidslot (13).
 16. The instrument according to claim 11, wherein the gasflow directing means are provided for directing a further part of saidhousing gas flow for said discharge through said slot (13).
 17. Theinstrument according to claim 2, provided with a centrifugal separator(5) for separating the gas into a clean and a polluted fraction, andwherein the gas supplying means (8) is connected close to the outerperiphery of the centrifugal separator (5), and the gas directing meanscomprises a connection adjacent the center of said separator (5),wherein means for the discharge of the polluted fraction is connected tosaid device (10) for said discharge of said fraction through said slot(13).
 18. The instrument according to claim 3, provided with acentrifugal separator (5) for separating the gas into a clean and apolluted fraction, and wherein the gas supplying means (8) is connectedclose to the outer periphery of the centrifugal separator (5), and thegas directing means comprises a connection adjacent the center of saidseparator (5), wherein means for the discharge of the polluted fractionis connected to said device (10) for said discharge of said fractionthrough said slot (13).
 19. The instrument according to claim 10,provided with a centrifugal separator (5) for separating the gas into aclean and a polluted fraction, and wherein the gas supplying means (8)is connected close to the outer periphery of the centrifugal separator(5), and the gas directing means comprises a connection adjacent thecenter of said separator (5), wherein means for the discharge of thepolluted fraction is connected to said device (10) for said discharge ofsaid fraction through said slot (13).